With laser disc players wherein optical video discs are used as signal recording media, a laser beam spirally traces the signal recording surface of the disc from inner periphery toward outer periphery for signal reproduction. There are two kinds of optical discs for use as signal recording media in laser disc players in respect of the signal recording method: CAV (constant angular velocity) discs wherein video signals are recorded at a constant angular velocity for two fields per turn of track, and CLV (constant linear velocity) discs wherein video signals are recorded at a constant linear velocity.
With the CAV disk, video signals for one frame are recorded per revolution, and the synchronizing signals included in the video signals are arranged on a radial line. Accordingly, a still picture can be readily reproduced by causing the pickup to jump back by one turn of track toward the inner periphery of the disc every time the vertical synchronizing signal for a specified odd-numbered field is reproduced while rotating the disk at a constant speed, for example, at 1800 r.p.m.
With the CLV disc, however, synchronizing signals are recorded on a spiral track at equal spacings and are not aligned radially of the disc, so that even if the pickup is caused to jump back by one turn of track every time the vertical synchronizing signal for a particular odd-numbered field is reproduced, the specified portion of the track will not always be reproduced.
Accordingly, a video disc player has been proposed which is adapted to reproduce a still picture from the CLV disc by repeatedly causing the pickup to jump from a first position to a second position preceding the first position by approximately one frame while detecting these first and second positions so as to intermittently output the signals of one frame recorded in the track portion of second position through the first position (Unexamined Japanese Patent Publication SHO 58-139577).
However, the proposed video disc player requires a complex circuit for detecting the first and second positions. Moreover, the jumping action of the pickup for still-picture reproduction makes discontinuous the color subcarrier which is prepared based on the color burst extracted from the reproduction video signal, giving rise to the problem that a color loss occurs in the picture reproduced.
With advances in video memory techniques in recent years, on the other hand, inexpensive field memories have been developed which are capable of storing video signals for one frame. The use of such a field memory in video disc players has been investigated to realize various modes of special reproduction.
Nevertheless, with field memory application techniques heretofore known generally, the period of writing video signals in the field memory and the period of reading out the signals therefrom (hereinafter referred to as a "writing-reading period") are both set to 262.5 times the field period, i.e. one horizontal synchronization period H, so that the application of the field memory to video disc players encounters the following problem.
When video signals for one field are written in the field memory with the period of 262.5H and are thereafter repeatedly read out from the memory with the period of 262.5H, for example, for reproducing a still picture, the writing-reading period includes the fraction of 0.5H, which therefore disturbs at the junction of fields the period of horizontal synchronizing signals included in the video signals to be reproduced to produce a skew.
Further with reference to FIG. 4 (b), the color subcarrier corresponding to the video signals of the 1st H through the 262nd H can be stored in the field memory with respect to the entire period of each wave, but the rear portion of the last wave of color subcarrier corresponding to the video signal of the 263rd H will not be stored in the memory. Accordingly, when the video signals are repeatedly read out of the field memory, the color subcarrier becomes discontinuous at the portion indicated at N in FIG. 4 (b) to result in a loss of color.
To overcome this problem, a video disc player has been proposed which is equipped with a highly responsive servo circuit capable of absorbing a time-axis error involved in synchronizing signals due to jumping and which is adapted to detect a discontinuity occurring in the color burst to delay the output signal to the display unit based on the detection signal ("TV Gijutsu (TV Techniques)," January 1987, pp. 96-100). The video disc player, however, has the problem of necessitating a complex circuit for detecting the discontinuity of the color burst.